This invention relates to liquid soil conditioners for agricultural use and more particularly to liquid soil conditioners comprising of aqueous suspensions of non amporhous calcium carbonate. The invention also relates to methods of treating agricultural land to improve its productivity.
Many soils have what is known as poor structure. This is characterised by low water penetration, surface crusting when dry, restricted root growth of plants and poor germination of seeds. It is desirable to improve soils having poor structure. Soils may also be deficient in that their acidity is too high, i.e. the pH is too low. For many agricultural uses a pH of about 6.5 is considered optimum. Many soils are acid with pH of 5.5 or less. It is hence desirable to raise the pH of acid soils.
It is known that a high sodium content in the soil is a primary cause of poor structure. When a soil with high sodium content becomes wet, very fine clay particles disperse into the soil water. They are transferred with this water and settle out in the fine pores between the soil particles. This causes the pores to become blocked. The soil becomes dense, and the movement of water, air, plant roots and tillage equipment is significantly hindered. This reduces the productivity of whatever crop or pasture is growing on that area. Clay soils fall into this category of soils.
Gypsum which is calcium sulfate has traditionally been used to improve the friability or structure of clay soils by reducing the sodium levels in the soil. The calcium ions formed from the disassociation of the gypsum displace the sodium ions from the surface of the clay particles. The sodium can then be eluted through the soil. The bound calcium allows the clay particles to link into a lattice network of particles resulting in a more open soil structure. 
Typically gypsum is used in a granular form and must be applied at very high rates, commonly about five tonnes per hectare in heavy clay soils. It can therefore be difficult and expensive to spread.
Furthermore, it is not feasible to apply bulk gypsum in many situations, as the spreading equipment is too large. For example, in many vineyards the rows of vines are too close together to allow access for a large vehicle.
A further problem with granular gypsum is that it may take twelve months or more to become effective as the particle size is relatively large. The effectiveness of the gypsum in exchanging the sodium ions in the clay is directly related to the surface area of the gypsum exposed to the clay. Finer particles have a greater surface area than larger particles for the same given weight of gypsum.
Gypsum particles are typically of the order of 1 mm diameter (1000 micron) or more. Although, finer particles could be produced by milling, the gypsum dust produced by this process can cause difficulties in application. Furthermore, the application of granular gypsum can cause soil compaction from the spreading machines. The spreading machines are usually heavy as they carry several tonnes of gypsum. The compaction caused by the tyres can be substantial. Those areas which become compacted are difficult to be planted with crops unless the soil is further tilled and returned to its uncompacted state.
Other products which can be used to displace sodium ions are available as alternatives to gypsum, but they have major disadvantages. For example, sulfur may be applied to soil for conditioning purposes. Sulfur undergoes microbial oxidation in soil to form sulfuric acid which in turn may react with lime (if any) present in the soil to form calcium sulfate, gypsum. It is usually only added to soil if it is deficient in sulfur. However, sulfur powder is generally difficult to spread. 
Sulfuric acid may also be directly applied to soil. Upon application to soils containing calcium carbonate, it reacts to form calcium sulfate. However, being a strong acid, it is difficult to work with, requiring special acid resistant equipment. Calcium chloride forms calcium ions on addition to soil and these displace the sodium ions in the clay in the same way as the calcium ions from gypsum do. However, the residual product from this reaction is sodium chloride. Salinity is already a major problem in many agricultural areas and, for most users, the application of calcium chloride is not a viable option to address a clay problem. 
With regard to the treatment of acid soils, one method used is to apply granulated limestone (CaCO3). However, the usual particle size of this material leads to the material having to be applied at very high rates. Furthermore, with this known treatment the pH tends to change relatively slowly, taking up to twelve months to lead to significant improvements. The requirement of large application rates causes similar difficulties to those discussed earlier for the application of gypsum.
Other methods have been proposed to improve the agricultural productivity of soil by adding soil conditioners.
Australian Patent 691460 discloses the application of an aqueous dispersion of calcium carbonate in a special precipitate form. A number of additives may be included in this formulation and these include well known agricultural materials such as herbicides, insecticides, metals and chelates. Sulfur is also mentioned as an optional additive when the soil is deficient in sulfur. The purpose of these compositions is to increase the pH of the soil. The relative quantities of the additives are not set out.
French Patent 2372131 relates to a special blend of three ingredients, two of which are sulfur and calcium carbonate. The volume ratio of calcium carbonate to sulfur in their blend is 3 to 1.
Canadian Patent CN 1113221 and CN 11136028 disclose foliar spray compositions for agricultural use. These are quite different from the soil applied soil conditioner of the present application.
Australian Patent 630806 discloses agricultural compositions based on deposit lime. In this patent they claim much greater efficacy for deposit lime compared to rock lime. They state that rock lime is essentially ineffective when used in their aqueous slurries.
The object of the present invention is to avoid some of the problems associated with the use of the above products.
This invention provides in one form a liquid soil conditioning composition in the form of an aqueous dispersion of calcium carbonate and sulfur wherein the atomic ratio of calcium to sulfur is in the range 0.5:1 to 2.0:1.
Preferably the atomic ratio of calcium to sulfur is in the range 0.75:1 to 1.5:1.
More preferably the atomic ratio of calcium to sulfur is in the range 0.9:1 to 1.3:1.
Preferably the composition includes a suspension or dispersing agent.
Preferably the suspension or dispersing agent is selected from bentonite and polyvinylalcohol.
Preferably the calcium carbonate is in non amorphous form.
More preferably the calcium carbonate is rock lime.
In an alternative form this invention provides a liquid soil conditioning composition comprising rock lime suspended in water wherein the rock lime has particle size average diameter less than 10 xcexcm with maximum particle size 50 xcexcm.
Preferably the average diameter is less than 5 xcexcm with maximum particle size 25 xcexcm.
Preferably the composition further comprises a suspension or dispersing agent that is a water soluble polymer.
Preferably the water soluble polymer is polyvinylalcohol. Preferably the composition comprises 700-1000 g/litre of water of calcium carbonate.
Preferably the amount of calcium carbonate is about 900 g/litre of water.
In a further alternative form this invention provides a method of improving soil agricultural productivity of clay soils without substantially changing the pH of the soil by applying an effective amount of a liquid soil conditioning composition in the form of an aqueous dispersion of calcium carbonate and sulfur wherein the atomic ratio of calcium to sulfur is in the range of 0.5:1 to 2.0:1.
In a still further form this invention provides a method of increasing the pH of agricultural soils by applying an effective amount of a liquid soil conditioning composition comprising rock lime suspended in water wherein the rock lime has particle size average diameter less than 10 xcexcm with maximum particle size 50 xcexcm .